Our long term research objective is the study of cardiac dynamics. This research project is designed specifically to study the dynamic determinants of left ventricular filling under normal and pathological conditions using the technique of transmitral phasic flow measurement. This approach yields valuable information on the physiology and pathophysiology of atrio-ventricular function and dynamics when combined with the measurement of other hemodynamic parameters: aortic flow, intracardiac pressures, electrograms, echographic visualization of the mitral valve and ventricular diameter, ultrasonic measurement of ventricular geometry, and thermal washout determination of ejection fraction. The experimental approach is designed to investigate, on a beat-to-beat basis, the following determinants of left ventricular filling: 1) phasic left ventricular relaxation rate; 2) left ventricular dynamic diastolic compliance; 3) mitral valve motion; 4) contribution of atrial systole; and 5) atrial reservoir function. These five areas will be investigated under diverse physiological conditions of heart rate, P-R interval, and functional state of the heart; and under three pathological conditions: 1) acute mitral regurgitation; 2) acute mitral stenosis and mitral annular constraint; and 3) abnormalities of rhythm. Although highly invasive, the measurement of phasic transmitral flow when coupled with simultaneous measurement of aortic flow, is the only direct method of determining ventricular volume changes thereby permitting the continuous determination of left ventricular compliance. Since it is also an accurate method, we anticipate that our results might offer definitive solutions to several significant problems related to ventricular filling and subsequent cardiac function which have heretofore been approached only by indirect and inferential means. Elucidation of atrio-ventricular dynamics in a way not possible by other means should also permit a more meaningful interpretation of the results of cardiac catheterization and non-invasive clinical methods, such as echograms.